This invention relates generally to optical instruments and more particularly concerns holders for securing an eyeglass frame without lenses into a specific fixed position so that the inside contours or shapes on the rims of the frame may be measured for the purpose of grinding the lenses to precisely fit the rims.
In the measurement of rim contours, the frame is generally secured in a fixed position in a frame holder and a stylus passes along the internal perimeter of each of the rims to determine their coordinates. The data thus collected is then used in the grinding of the appropriate lenses.
Presently known frame holders suffer from a variety of inadequacies. They are generally very complex and, therefore, both initial and maintenance costs are relatively high. They are complicated and confusing in operation, requiring a dexterous manipulation of the frame within the holder to achieve proper positioning with simultaneous operation of a multiplicity of adjusting mechanisms to secure the frame in the selected position. The result is a procedure which clumsy, inconsistent and frustrating. Furthermore, the securing mechanisms frequently cause distortion of the rims, rendering the measured data inaccurate and the lenses imprecise. The amount of this distortion of the rims tends to increase proportionately to the degree of frustration experienced in trying to secure the frame in the holder. These inaccuracies are further compounded because the frames are typically centered in the holder in reference to nose pads which are generally flexible or adjustable, thus resulting in inaccurate centering for the grinding process. Moreover, the stylus generally accumulates only two dimensional data. Consequently, when the perimeter of an individual rim does not lie in substantially a single plane, inaccuracies result. This inaccuracy is multiplied when the rim planes and frame plane are different. That is, known frame holders secure the frame in a plane substantially parallel to the base plane of operation of the stylus, and of the planes of the individual rims are not coincident with the plane of the frame, or unnecessary inaccuracy is introduced into the data collected.
It is, therefore, an object of this invention to provide a frame holder of relatively simple construction. It is a further object of this invention to provide a frame holder that lends itself to easy and consistent operation. Another object of this invention is to provide a frame holder that requires minimal dexterity in securing the frame. A further object of this invention is to provide a frame holder which minimizes distortion of the frame in its secured condition within the holder. It is also an object of this invention to provide a frame holder which centers the frame in relation to the rims and not in relation to the nose pads. Similarly, it is an object of the present invention to provide a frame holder that accurately centers the frame in the holder. It is a further object of this invention to provide a frame holder that permits adjustment of the orientation of the rims in the holder to minimize the occurrence of two dimensional error in the measuring process. Another object of this invention is to provide a frame holder contoured to facilitate accurate location of the frame within the holder.